Method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex



Aug. 15, 1950 A. M. THOMSEN 7 METHOD OF REGENERATING A SPENT COOKING LIQUOR RESULTING mom THE DIGESTION OF A CELLULOSE-LIGNIN coupmx Filed July 25. 1947 aellmlose "14 9111622 flmplaac 1 II M .11, 11 u FOL-Mm;

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Patented Aug. 15, 1950 UNITED STATES PA-TE .orriics METHOD 1F IREQENERATING A COOKING .LIQUQR RESULTING FROM THE ,DIGESTIQN OF A 'CEI LULOSE- ILIGNIN COMPLEX Alf-red M.' I-homsen, San Francisco. Calif.

Application Juli 23, ScrialNo; 163,087

*7 Glaims,

Th un l ing ch m cal reaction upon which my oce s i based is the selective action r the allgaline metal sulphides upon the lignin ingredient of such complexes" while :the cellulose comcnentis but sli htly afiected, Simultaneously,

the components that would consitutc the socalled tether extract of such complexes are saponified or emulsified by the action of the sulphide and thus pass into the li nin solution together withsaid lignin. 7

While these statements are but well known facts i-iamiliar to .all that are skilled in the art yet little use has been made thereof because of the lack of a truly cyclicma-nner of recovering and reusing the all essentiasl alkali :metalsulphide,

It is, theref re, i furnishin such a truly cyclic recovery and reuse that :my process "resides, not

in the orthodox chemistry :on whichit is based.

The expr ssion "alkali metal sulphide rin cludes, of course, both potassium and sodium sulphide. In general, the potassium salt is the better but the sodium salt the cheaper, but many of these complexes contain considerable potas slum so that even though the "process be started with'sodium sulphide yet the re cycled medium will =.ulti1nately become a -=mixtureof salts of bo'th sodium andpotassium.

:Myiprocess Jhence consists in digesting a comminuted form :of the complex '-with a re-cycled solution of alkali metalsulphideat a temperature range corresponding to a gage pressure of from 20 to 125 pounds, depending upon the character of :the complex, tor-such a time as shall 'benee'ded to f li'loerate the cellulose component from the encrusting materials.

Inthe accompanying flowsheetI have set forth the various steps needed to accomplish the reuse of said sulphide and the "process "is best followed and understood by the complete explanation of saiddrawing. However,;a=brief synopsis will first be given. Separation is first made between the solid and liquid components of the completed digestion. The spent'cooki-ng liquor-is then acidifled with sulphur dioxide, thus converting the resident alkali metal salts substantially into sulphates and sulphites, chiefly the latter. This is accompanied by the separation of sulphur and of V a modified form o'r lignin, as well as the ingredients constituting the ether extract. The "resuitant solution, after removal of the ingredients above-mentioned, is theneva-porated and the resident salts converted to sulphide by a reducing furnace operation in the'presence of solid carbon pr or materials that will yield solid carbon. The.

2 reduced salts are dissolved in water and then constitute the cooking liquor as originally empl y d- While this is the essence of the process, anumber of additional steps appea in the drawing, They are introduced to facilitate the above de. scribed series of reactions and to the extent .110 which they contribute additional revenue ,from

ymroclucts are of much commercial impontance.

version of my P ocess a applied to the resinous stump wood of certain :pines that are rich in resinous material, sucfhzas the southern pine, the sugar pine and the 'ponderosa :pine. Such woocl will contain over 20% -.of resinous material and included in the ether extract will he a varying amount of fatty acids, partly free and partly as fats, chiefly 'oleic acid.

This maw'rmaterialis chipped as in conventional pulp work and then digested for a period of 5 hrs. at a pressure of "85 lbs. gage, with an adequate amount solution to cover same. The cool:- ingiliq'uor will contain approximately of the bone dry weight of wood as Nags. When digestion is completed the pulp is separated from the ,spentcoo'king liquor a'nd thelatter'saturated-with a gas containing a substantial portion of EQz, such as spent boiler stack gases, or lime ikiiln gas.

"The saturation is effected by scrubbing or by blowing the compressed gas throughthe liquid. A

heavy precipitate of a modified form of ligninis separatedand removed in'the separator, which maybe a settler, a filter, or a centrifuge, as desired. -On "the drawing this Jign'in is seen later on commingled with the mix for the iurnace, .but

if a better commercial use is desired such use can e ep aced by mos any substance that will yield solid carbon in the iurnace operation, such as waste vegetable matter.

The time for such saturation .cannot be aspecified butit is continued until a filtered sample of the liquor yields almost no additional -precipitate with fresh 102. The reason :for this preliminary saturation with CO2 is to obtain resinous r fatty d c m nents :the next step,

a more concentrated form than would be the case if commingled with all this lignin which has now been removed.

The liquor, purified by the removal of said lignin, is next saturated with a gas containing a substantialamount of S02, such as the spent gas from thereducing furnace operation, roaster gas from the roasting of metallic sulphides, or purer forms of S02. quantitative and is continued until the liquor shows no alkaline reaction when the separation of the resinous and fatty acids will be found complete This is likewise done bytest. Commingled with the resinous and fatty materials will also be a certain amount of highly degraded lignin.

After separation from the liquor, this ether.

extract is purified by the use of a selective solvent which will leave the lignin behind. As the,

separated acids are soluble in virtually all types of fat solvents the greatestvariation is possible. Any of the alcohols, acetone, or chlorinated derivatives are acceptable. Also ethers and the light petroleum distillates. On the drawing I have shown the cyclic use of such a solvent by the use of a still which is, of course, conventional. The, lignin residual is sent to the furnace as in the former case.

The residual solution from the S02 saturation is next evaporated to the highest degree compatible with retaining a fluid material. t is then :mixed with the separated lignin residuals, or in lieu thereof with a substance that will yield solidC in the furnace step. The operation in the furnace is entirely reducing, so a reducing flame is used as the source of heat and an excess of solid C is maintained. This excess is cyclically returned from the dissolving step. I have also shown the use of CaCOa in the furnace charge. This is not absolutely essential and may be omitted. It will be seen that it is also cyclically returned. In the furnace operation it becomes converted to Gas, but in the lixiviation step it becomes reconverted to CaCOa. Its advantage is largely mechanical, as it makes a sm-oothoperation. About 50% on the charge is alkali metal sulphides, is the best Warrant for an adequate temperature. Any increase in unreduced alkali metal sulphites and/or sulphates is the signal that the temperature must be increased.

T-he output of the furnace is discharged directly into water where its soluble ingredients dissolve. Separation is then made, by settling or otherwise, of the solids which are chiefly CaCOs, excess C, and minor decomposition products. In as much as impurities are continually introduced in the raw material the cyclic load is gradually rendered more and more impure. It must, therefore be discarded periodically or else a small amount must be split off consistently and replacement material added to make good. the.

loss. 'Unless the content of alkali salts in the raw material is adequate there will likewise be a need for some'replacement of the sodium sulphide with which the operation was commenced. This is most convenientlycovered by adding the corresponding sulphate to the mixer.

Any type of furnace may be used for this reduction but I prefer the use of a rotary furnace,

The absorption is virtually I similar to a cement kiln. A separate fire box will be needed and the discharge end of the furnace must be closed in order to insure a reducing atmosphere within the furnace.

The temperature in the dissolving tank should be near boiling. If it drop too low there is danger of carbonates appearing in the cooking liquor which is the sign of undecomposed Na2S being returned with the cyclic load. A little does no harm but the content should be substantially sulphide, so any increase in carbonate means lack ration with S02. thus be obtained.

It is also obvious that the furnace gases could of temperature in the dissolver.

wax would be a substance very similar to beeswax, and it would be obtained from the centrifuge in a very concentrated form easy to subject to additional refining.

While not represented on the drawing, it is obvious that concentration by evaporation could be introduced anywhere before the furnace without changing any other sequence. If it preceded the first saturation then a soap would rise to' the surface of evaporator storage tank, and such soap could be easily skimmed off. The composition of said soap would be higher in fatty acids and lower in abietic than the material remaining in solution and subject to recovery after satu- A partial fractionation could be made the source of both the S02 and the CO2 needed in the saturation steps and that the above result would be obtained if the spent cooking liquor were passed counter-current to the furnace gases, lignin being separated after the first saturation with CO2, and fatty material from the latter saturation. After the gases had contacted the liquor the S02 resident therein would have been quantitatively absorbed and only CO2 would remain for the subsequent use of the gas in saturation.

Inasmuch as cellulose-lignin complexes with additive ingredients of resins, fats, fatty acids, and waxes run almost the entire gamut of the vegetable world it is evident that the two illustrations given herein represent but an exceedingly small fraction of the total field. In general, therefore, it may be said that trial and error.

'must be the means whereby a process, conceived within the limits of this disclosure, is made adaptable to any type of raw material falling within the scope of my process. Such adaptations, or modifications, will be found to represent little except a sound knowledge of the chemistry involved and will suggest themselves to any operator.

Having thus fully described my process, I

claim:

tralizing said liquor with sulphur dioxide; removing the materials rendered insoluble by said neutralization; evaporating the neutralized liquor; commingling it with material containing carbon; incinerating the mixture in a reducing atmosphere to convert resident alkali metal salts to sulphide; lixiviating said reduced incinerated material to obtain a solution of alkali metal sulphide suitable for another digestion of celluloselignin complex.

2. The method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex with an alkali metal sulphide as the sole, active ingredient which comprises; commingling said spent cooking liquor with carbon dioxide as long as a precipitate of lignin is pro- .duced thereby; separating the lignin from the residual solution; neutralizing said resultant solution with sulphur dioxide and removing the ingredients rendered insoluble by such neutralizing procedure; evaporating the neutralized liquor after separation of the insoluble ingredients; commingling it with material containing carbon; incinerating said mixture in a reducing atmosphere to convert resident alkali metal salts to sulphide; lixiviating said reduced incinerated material to obtain a solution of alkali metal sulphide suitable for the digestion of a cellulose-lignin complex.

3. The method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex with an alkali metal sulphide as the sole, active ingredient set forth in claim 1; with the added step that calcium carbonate be added to the mixture being incinerated; the solids from the lixiviation step, containing said calcium carbonate and excess carbon, being cyclically returned to the mixture before incineration.

4. The method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex with an alkali metal sulphide as the sole, active ingredient set forth in claim 2; with the added step that emulsified solids suspended in the spent cooking liquor be separated prior to the treatment with carbon dioxide recited therein.

5. The method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex with an alkali metal sulphide as the sole, active ingredient which comprises; re-

moving any emulsified substances suspended in said spent liquor; saturating the residual liquor with carbon dioxide as long as any lignin is precipitated; removing said lignin; saturating the liquor after such lignin removal with sulphur dioxide until liquor is no longer alkaline; separating the material rendered insoluble in such saturation; evaporating the neutralized liquor and commingling it with lignin previously separated and a cylic return of solids from a future lixiviation step; incinerating said mixture in a reducing atmosphere to convert resident alkali metal salts to sulphide; lixiviating said reduced incinerated; material to obtain a solution of alkali metal sulphides suitable for the digestion of a celluloselignin complex and residual solids; and returning the solids to the mixture to be incinerated as previously specified.

6. The method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex with an alkali metal sulphide as the sole, active ingredient as set forth in claim 5; with the added step that calcium carbonate be made an ingredient of the solids cyclically returned from the lixiviating step.

7. The method of regenerating a spent cooking liquor resulting from the digestion of a celluloselignin complex with an alkali metal sulphide as the sole, active ingredient as set forth in claim 5; with the added step that saturation with CO2 and S02 as disclosed-therein be effected by passing the spent cooking liquor counter current to the gases obtained by the oxidation of the volatile products obtained in the incineration step.

' ALFRED M. THOMSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,689,534 Richter Dec. 4, 1928 1,743,080 Bradley et al Jan. 7, 1930 1,797,678 Bradley et al Mar. 24, 1931 1,860,803 Bradley et a1 May 31, 1932 1,864,619 Richter June 28, 1932 2,201,797 Scott May 21, 1940 

1. THE METHOD OF REGENERATING A SPENT COOKING LIQUOR RESULTING FROM THE DIGESTION OF A CELLULOSELIGNIN COMPLEX WITH AN ALKALI METAL SULPHIDE AS THE SOLE, ACTIVE INGREDIENT WHICH COMPRISES; NEUTRALIZING SAID LIQUOR WITH SULPHUR DIOXIDE; REMOVING THE MATERIALS RENDERED INSOLUBLE BY SAID NEUTRALIZATION; EVAPORATING THE NEUTRALIZED LIQUOR; 